1. Field of the Invention
The present invention relates generally to the field of voice over packet (VoP) telephony, and more particularly to providing intelligent network control services in IP telephony.
2. Technical Background
For most of the past century or so, most telephony services have been provided by circuit switched networks. Packet switched telephony is a relatively recent development. For example, Internet telephony began in the mid 1990s with the introduction of Internet phone software. Internet telephony is the real-time delivery of voice, and other multimedia data, between two or more parties across a network using Internet protocols (IP). Internet phone software is designed to run on a personal computer equipped with a sound card, speakers, microphone, and modem or directly coupled to the internet via a LAN. Software compresses the voice signal and translates it into packets for transmission over the Internet. This basic PC-to-PC Internet telephony works, however, only if both parties are using Internet phone software.
Internet telephony, or voice over an IP network (VoIP), offers the opportunity to design a global multimedia communications system that may eventually replace the existing circuit switched telephony infrastructure. In a relatively short period of time, Internet telephony has made significant advances. Many software developers now offer PC telephony software. Internet telephony involves establishing a communications session between two logical addresses in the network. Generally, a first Internet protocol, such as H.323 or Session Initiation Protocol (SIP) is used to establish the session and negotiate the capabilities for the session, and a second Internet protocol, such Real-time Transport Protocol (RTP), is used to transport the actual media across the IP network.
While packet switched telephony offers benefits to both users and carriers in terms of cost and variety of media types, there is a substantial installed base of traditional telephones served by the public switched telephone network (PSTN). Moreover, in addition to its widespread nature, the PSTN offers a rich set of intelligent network services such as “800” number services, Virtual Private Network (VNET) services, call forwarding, and the like. IP telephony and the PSTN will co-exist for a period of time. Thus, there is a desire to integrate the PSTN with IP networks, including the Internet and private intranets.
The evolution of the integration of the PSTN and packet-switched telephony can be seen in FIG. 1 and FIG. 2. FIG. 1 shows two separate self-contained networks, PSTN 100 and packet-switched network 1. Each includes separate call control resources, and each includes separate transport facilities. In the example depicted in FIG. 1, PSTN 100 provides virtual private network (VNET) services for a customer having two sites. A circuit is established between PBX 14 and PBX 14′ by way of switches 102. Dial plan information, number translations, and all of the other call control data required to maintain the VNET is provided by legacy service control entity 40. Packet-switched network 1 allows packet-switched telephony sessions to be established between IP telephones 18 and IP telephones 18′. IP telephones 18 are coupled to router 8, whereas IP telephones 18′ are coupled to router 8′. Call control is provided by call control proxy server 20. Location manager 30 stores dial plan information, user profiles, and other data required by control entity 20 to establish and maintain packet switched telephony sessions. While call control server 20 and location manager 30 may be implemented as shown, e.g., as two separate systems running on two or more hardware components, those of ordinary skill in the art will recognize that call control server 20 and location manager 30 may be combined into one logical and/or physical system. A SIP server is the generic term used for a server having the combined functionality of call control server 20 and the location manager 30.
FIG. 2 shows the first stage in forming an integrated network 10. Enterprise gateways 16 are introduced to couple PBXs 14 with router 8. Gateways 16 allow cross-over calls among telephones 12 coupled to PBX 14 and IP telephones 18. Both signaling and media translations are handled by gateways 16. Thus, calls originating at PSTN-based telephone 12, can be partially transported by IP network 1 for eventual delivery to a second phone, either IP telephone 18, or PBX telephone 12′, coupled to PBX 14′. Unfortunately, there are limitations to the integrated system depicted in FIG. 2. While the integrated network depicted in FIG. 2 permits calls to cross-over between networks, call control data is segregated and not shared by the individual networks.
One problem associated with the integrated system depicted in FIG. 2 relates to the difficulties associated with supporting a VNET (or other legacy system services) when the customer has facilities spanning both PSTN 100 and the IP network 1. One approach that has been considered is to maintain two intelligent network systems; one for each network. However, the use of duplicate intelligent network systems is problematic. Legacy call control entity 40 and location manager 30 must be synchronized at all times. Ensuring that both systems have identical sets of data is logistically very challenging. If one system diverges from the other system even momentarily, calls may be mis-routed, perhaps even being directed from one VNET to an entirely different VNET. Thus, it is desirable to support a given customer from a single body of call control data. Because the legacy call control system is well established, what is needed is a way of importing legacy based call control data into the IP network. However, there is a drawback associated with this approach.
In the PSTN, signaling information and message payloads (e.g., voice) are carried by different systems. One drawback to providing PSTN-based intelligent network services to IP telephony calls is related to the fact that both signaling information and message payloads are delivered by the same vehicle, e.g., a packet. As a result, IP telephony has several types of security issues that are not present in the PSTN. One type of security attack is commonly referred to as IP spoofing. IP spoofing is an attempt to gain access to the network, and network services, by changing a packet's IP address to make it appear that the packet came from a legitimate network address. Another security issue involves co-opting a session by manipulating a packet's header or IP data payload. What is needed is a secure method and system for providing all of the PSTN-based intelligent network services to IP telephony calls.